Electrical devices



June 29, 1965 J. L. SENDLES 3,

ELECTRICAL DEVICES Filed Nov. .19, 1963 United States Patent s 4 Claims. (Cl. 338-162) The present invention relates to electrical devices of the kind in which a movable contact member is arranged to bear upon and slide across or along a resistance element.

It is common practice to employ an electrical device of kind as an instrument for measuring the relative movement between two members of an apparatus and it is not uncommon to incorporate such devices in apparatus which may become subjected to vibration over very long periods, giving rise to excessive Wear of the resistance element and the contact member engaging it.

It is one object of the present invention to provide in an electrical device of the kind specified means whereby such wear can be avoided.

According to the present invention there is provided an electrical device comprising a resistance element, a movable contact member which is in operation arranged to bear upon and slide across or along the resistance element, and a supporting arm on to which the movable contact member can be placed so as to occupy a rest position in which it is held out of engagement with the resistance element. Preferably, the supporting arm is permanently electrically connected to the resistance element so that the continuity of the device can be tested with the movable member in the rest position.

One embodiment of the invention will now be described by way of example with reference to the accompanying drawing which is a schematic perspective view of a potentiometer according to a preferred embodiment of the invention. 8

Referring to the drawing there is provided a potentiometer having an annular resistance track 11 of conducting material disposed on a circular electrically-insulating base 12 and a wiper in the form of a bifurcated resilient metal arm 13 extending from a centrally located spindle 14 and terminating in a contact button 15 which, by virtue of the resilience of the arm 13, bears on the resistance track 11 and slides therealong when the spindle 14 is rotated.

The contact arm 13 is provided with an outwardly extending portion 16 so that the arm 13 can be turned and brought to a predetermined rest position in which the portion 16 of the arm is placed on the end portion 17 of a rigid metal supporting arm 18 extending tangentially with respect to the resistance track and being mounted at its end remote from the track on a brass block 19. A further metal arm 20 is mounted between the brass block 19 and an electrically insulating block 21, the two arms and the blocks 19 and 21 being secured to the base 12 at selected locations by a screw 22 which is insulated from the arms 18 and 20 by an insulating bush 23. The selectivity in securing this structure permits the rest position of the contact arrangement to be predetermined. The further arm 20 extends in a direction parallel to the supporting arm 18 and terminates at the track in a downwardly turned end portion 24 which resiliently bears upon the track over a small contact area. The supporting arm 18 and the track contact arm 20 are electrically connected together so that the wiper arm 13 is electrically connected to the track 11 when in the rest position.

When the apparatus incorporating a potentiometer as above described is to be transported under conditions in which it may be subjected to continual vibration, the wiper arm 13is moved to the rest position shown in the drawing so that the contact button 15 is clear of the potentiometer track. It is, of course, arranged that relative movement between the wiper arm 13 and the potentiometer track 11 when the potentiometer is brought into operation is sufficient for the wiper arm 13 to move clear of the end 17 of the supporting arm 18 and on to the track 11.

What I claim as my invention and desire to secure by Letters Patent is:

1. An electrical device comprising an electrically insulating base, a resistance element mounted on said base and provided with at least one terminal, a movable contact member supported by said base and operatively arranged to bear upon and slide with respect to the resistance element, and a supporting arm independent of said resistance element terminals and selectively mounted on said base to support said movable contact member at a predetermined rest position in which it is out of engagement with the resistance element, said supporting arm being positioned in relation to said element to cause said movable contact member upon release from the supporting arm to engage said element at a predetermined intermediate position on the element and to permit said movable contact member upon release from said supporting arm to move throughout the length of the resistance element without further contact with the supporting arm, and means associating with the supporting arm so as to automatically connect the movable contact member to the resistance element when the latter is in the said rest position on the supporting arm so that the continuity of the device can be tested with the movable contact member in the rest position.

2. A device according to claim 1, wherein said means provides an electrical connection from the predetermined intermediate position on the element to said movable contact member.

3. A device according to claim 2, wherein said supporting arm is electrically conducting and wherein said means comprises a further electrically conducting arm supported by said base, said further arm extending to the element and resiliently bearing thereupon, the supporting arm and the further arm being in electrical contact.

4. A device according to claim 3, wherein the resistance element is in the form of a resistance track of electrically conducting material disposed on said base and wherein the movable contact member comprises a wiper inthe form of an additional resilient electrically conducting arm carrying an electrical contact button which, by virtue of the resilience of the additional arm, bears on the resistance track and can he slid therealong when the wiper is moved.

References Cited by the Examiner UNITED STATES PATENTS 1,678,892 7/28 Wiegand 3381'50 2,405,689 8/46 De Giers 33833 X 2,463,045 3/49 Mucher 338-202 X 2,506,482 5/50 Batcheller 338-178 2,541,359 2/51 Huck 338-200 X 2,826,664 3/58 Ralston "338-173 X RICHARD M. WOOD, Primary Examiner.

ANTHONY BARTIS, Examiner. 

1. AN ELECTRICAL DEVICE COMPRISING AN ELECTRICALLY INSULATING BASE, A RESISTANCE ELEMENT MOUNTED ON SAID BASE AND PROVIDED WITH AT LEAST ONE TERMINAL, A MOVABLE CONTACT MEMBER SUPPORTED BY SAID BASE AND OPERATIVELY ARRANGED TO BEAR UPON AND SLIDE WITH RESPECT TO THE RESISTANCE ELEMENT, AND A SUPPORTING ARM INDEPENDENT OF SAID RESISTANCE ELEMENT TERMINALS AND SELECTIVELY MOUNTED ON SAID BASE TO SUPPORT SAID MOVABLE CONTACT MEMBER AT A PREDETERMINED REST POSITION IN WHICH IT IS OUT OF ENGAGEMENT WITH THE RESISTANCE ELEMENT, SAID SUPPORTING ARM BEING POSITIONED IN RELATION TO SAID ELEMENT TO CAUSE SAID MOVABLE CONTACT MEMBER UPON RELEASE FROM THE SUPPORTING ARM TO ENGAGE SAID ELEMENT AT A PREDETERMINED INTERMEDIATE POSITION ON THE ELEMENT AND TO PERMIT SAID MOVABLE CONTACT MEMBER UPON RELEASE FROM SAID SUPPORTING ARM TO MOVE THROUGHOUT THE LENGTH OF THE RESISTANCE ELEMENT WITHOUT FURTHER CONTACT WITH THE SUPPORTING ARM, AND MEANS ASSOCIATING WITH THE SUPPORTING ARM SO AS TO AUTOMATICALLY CONNECT THE MOVABLE CONTACT MEMBER TO THE RESISTANCE ELEMENT WHEN THE LATTER IS IN THE SAID REST POSITION ON THE SUPPORTING ARM SO THAT THE CONTINUITY OF THE DEVICE CAN BE TESTED WITH THE MOVABLE CONTACT MEMBER IN THE REST POSITION. 